As is known, magnetic field sensors are used in a variety of applications. One example application is in motion (e.g., rotation) detectors where a magnetic field sensor is used to detect motion of an object, such as a ferromagnetic object, for example, a gear or ring magnet. In motion detectors, the magnetic field is typically detected by one or more magnetic field sensing elements, such as Hall effect elements or magnetoresistance elements, which provide a signal (i.e., a magnetic field signal) proportional to a detected magnetic field.
Some motion detectors generate an output signal indicative of the speed of motion of the object. Other motion detectors generate an output signal indicative of a direction of motion of the object as well. One such motion detector is described in U.S. Pat. No. 8,624,588 entitled “Apparatus and Method for Providing an Output Signal Indicative of a Speed of Rotation and a Direction of Rotation as a Ferromagnetic Object,” which is assigned to the assignee of the present disclosure and incorporated herein by reference in its entirety.
Motion detectors are widely used in automobile control systems, for example to detect motion of a target object (e.g., camshaft) and to provide information (e.g., an absolute angle of rotation of the target object) to an engine control processor for ignition timing control, fuel management and other operations. With this information, the engine control processor can adjust the timing of firing of the ignition system, the timing of fuel injection by the fuel injection system and perform other operations.
In high precision applications such as automobiles, accuracy variations in the detected motion of a target object (e.g., resulting from irregularities in a sensed target profile of the target object) can be problematic. Engine ignition timing, for example, depends on consistent detection accuracy. Some magnetic field sensor integrated circuits (ICs) contain circuitry and methods to mitigate the effects of irregularities resulting from mechanical variations such as rotational wobble or changes in an airgap between the IC and the target object.